1. The problem statement, all variables and given/known data sorry for the long question. 2. Relevant equations 3. The attempt at a solution I get everything up until it asks where the extra "half" of the power is spent. I do know that the extra half is referring to the "2" dK/dt. I have spent the last hour or so thinking about this while working the chapter practice problems out, just in case i glimpse a moment of realization by thinking about energy. Unfortunately no. Since this is not a "homework problem" could someone just explain why it is 2dK/dt and not the more logical dK/dt? Energy lost during collision of sand with belt? perhaps something to do with the fact that the belt is a belt and not a plane moving perpetually right?